1. Field of the Invention
The present invention relates to a suspension apparatus of a vehicle adapted to change suspension characteristics.
2. Description of Related Art
Recently, as a suspension apparatus of a vehicle is called an active suspension, it is proposed that the suspension apparatus is of a type in which its suspension characteristics can be changed in an arbitrary manner. The so-called active suspension is basically constructed such that a cylinder unit is interposed between an unsprung weight and a sprang weight and that the suspension characteristics are controlled by controlling a supply and discharge of operating liquid to and from the cylinder unit. Japanese Patent Publication (Kokoku) No. 14,365/1984 discloses a suspension apparatus which uses a cylinder unit as an actuator for adjusting a height of the vehicle body and which controls a posture of the body by controlling a magnitude of the operating liquid pressures in the cylinder unit.
Such an active suspension as have been disclosed is basically constructed such that a posture of the body is controlled to take a desired posture in terms of bouncing, pitching and rolling, by controlling a height of the body at the positions of the wheels by means of each of the cylinder units.
This posture control can permit a favorable control over a posture of the body itself, however, it might impair ride comfortableness because the vehicle body is pushed up from pavement to a large extent. In order to carry out the posture control without largely impairing ride comfortableness, it may be possible to control acceleration in a vertical direction so as to become as small as possible. Japanese Patent Publication (kokai) No. 139,709/1984 discloses a suspension apparatus in which an air spring is used as an actuator for adjusting a height of the vehicle body and a posture control of the body is carried out while ensuring ride comfortableness, using acceleration in a vertical direction and a differential value of the acceleration in the vertical direction as parameters, while ensuring a ride comfortableness.